1. Field of the Invention
According to exemplary and non-limiting embodiments, the present invention relates to a door approach communication apparatus for irradiating a searching radio wave in the vicinity of a vehicle door. The invention also relates to a wireless-type door lock control apparatus using the door approach communication apparatus. More particularly, the invention relates to an unlock transmitting apparatus provided with, in a vehicle having an electrically driven door lock device, an antenna, a transmitter, a receiver and a door lock controller. This apparatus irradiates a searching radio wave via the transmitter and the antenna and sends an unlock signal to the electrically driven lock device when the receiver decodes an unlock signal. The apparatus employs a search and answer style of interrogation in which, when the searching radio wave is received by a portable wireless device held by a driver, an unlock signal radio wave is transmitted therefrom.
2. Description of Related Art
Transmitting apparatus for automatically unlocking the doors of vehicles are generally referred to as keyless entry systems. According to the keyless entry system disclosed in Japanese Unexamined Patent Publication No. 60-119873 and Japanese Unexamined Patent Publication No. 9-22429, a receiver located on a vehicle and a loop antenna for communicating with a portable wireless transmitter held by a driver are used. The loop antenna is formed by a conductive print pattern at a peripheral edge portion of a door mirror or on the surface of a door window.
According to the keyless entry system disclosed in Japanese Unexamined Patent Publication No. 9-32378, an antenna is installed in the vicinity or at the inside of an outside door handle. In this case, a receiving region is constituted by an area in the vicinity of the driver's seat door.
According to the above example of using a loop antenna, an antenna (coil) is mounted to a part located on the vehicle, such as by embedding an antenna coil inside a door mirror or pasting an antenna on the surface of a door window. Accordingly, the cost of implementing this apparatus may increase. Further, the parts used in implementing this apparatus may be large in size, and the characteristic of the antenna is liable to suffer influence from the surrounding parts. This design may also suffer from other drawbacks.
It may be less problematic to mount an antenna in the vicinity or inside an outside door handle when the outside door handle is made of resin. However, when the outside door handle is made of a metal (for example, made by zinc die-cast) as well as when a metal is coated on the surface of the resin, the function of the mounted antenna may be hampered.